The present invention relates generally to printing presses and more particularly to printing presses having printing sleeves that are placed on or removed from a cylinder with the aid of air or other fluid pressure.
Tubular-shaped printing sleeves, such as offset lithographic printing blankets described in U.S. Pat. No. 5,215,013, are placed and removed axially over a printing cylinder. As described with respect to a blanket in the ""013 patent, air holes typically are located on a work side end of the blanket cylinder to provide pressure to the inside of the blanket as the blanket is removed or placed axially over the blanket cylinder.
However, blankets can become stuck when mounted for too long, as air pressure from the air holes can be blocked and not reach the gear side end of the cylinder. Moreover, the use of only one set of air holes on the work side end makes hole placement critical, or the sleeve will not inflate or expand at all. With improperly placed holes, the air may simply rush out of the work side end without inflating the gear side end.
Also, it may be desirable to place multiple blankets side-by-side over a single blanket cylinder. A single set of work side holes can inflate only one of the blankets at the work side, thus not permitting the other blankets closer to the gear side to be removed.
It has been attempted to place additional air holes along the length of the body of the printing cylinder. However, when the sleeve is in a partially removed or placed position, these air holes remain uncovered while the work side air holes are covered. A large pressure reduction results as the air rushes out the uncovered holes and the flow drops at the work side holes, thus making blanket placement or removal difficult or impossible. Thus the additional holes require the use of multiple plumbing fixtures, solenoids and valves to control the air flow properly. These features tend to be expensive and are complicated, especially because the cylinder must rotate.
In a 1981 textbook entitled, Beruehrungsfreie Dichtungen (Contactless Seals), the authors describe labyrinth seals, in which fluid flow can be blocked or reduced using vortices. In FIGS. 3-56 at pages 174-176, the effect of placement of fins on air flow and vortex generation is shown. However, the use of these seals in printing machines or for printing cylinders is not discussed.
U.S. Pat. No. 5,797,531 discloses a turner bar that has a hollow space that can be connected ti a compressed air source for deflecting a printed web of material. Air outlet openings are provided on a circumferential surface of the bar in an axial direction, through which openings air exits so that an air cushion builds between the surface of the turner bar and a web. Thus contact free guiding of the web is permitted. The individual air openings of the turner bar have opening and closing elements which act as valve elements that can open or close. In a first condition when the air opening is not covered by the web, compressed air flows out through a bore in the opening and closing element, the opening and closing element is thrust upward in a guide, until a closing cone closes a bypass system, and thus reduces the outflow of the compressed air. In a second condition, in which the air openings are covered by a paper web, the volume of air continuously emerging from the bore forms an air cushion. A counterpressure in the air outlet opening is generated by the air cushion, so that the opening and closing element retracts, and air passes through the bypass system. A greater volume of air then flows beneath the web.
U.S. Pat. No. 2,828,553 discloses a device for conditioning webs, in which a roller air openings on its circumference for aiding in transport of a web. The openings can be actuated by contact with a web, so that for example, a ball is held between curvilinear interior surfaces. As pressure is decreased or as the top of the ball protruding above the surface of its raceway is contacted by the web, the ball is depressed and the air can emerge about the spherical surface of the ball against the under surface of the web.
An object of the present invention is to provide a printing cylinder that can accommodate the fluid-assisted removal or placement of more than one printing sleeve. An alternate or additional object of the present invention is to improve the fluid-assisted removal or placement of a printing sleeve.
The present invention provides a printing cylinder for accepting an axially-removable printing sleeve comprising a cylinder body having an outer surface, the outer surface having at least one hole and a supply line in the cylinder body for supplying fluid to the at least one hole. The supply line has at least one flow restrictor altering fluid flow as a function of the at least one hole being covered by an axially-removable printing sleeve.
The fluid preferably is air, and the flow restrictor may form vortices when the at least one hole in uncovered.
The flow restrictor also may be a valve, which can become more open as a function of the axial position of the printing sleeve. The valves thus also can be provided so that a movement of the sleeve is not hindered by the valve, and so that friction is reduced. Extra control devices and sensors are not required.
The valve preferably is a ball-valve.
The outer surface may have a plurality of other holes at a work side end of the printing cylinder, with the at least one hole located axially between the other holes and a gear side end of the printing cylinder. The plurality of other holes may include another supply line having at least one other flow restrictor for the other holes.
The flow restrictor preferably includes a plurality of opposing fins, tips of opposing fins being spaced so as to form a free-flow channel.
The at least one hole preferably includes a plurality of holes, with the at least one flow restrictor including a flow restrictor for each hole.
The outer surface may include a second set of holes for a second axially-removable printing sleeve, the second set of holes having second flow restrictors.
The present invention also provides a printing press comprising a first printing cylinder having at least one external hole and a first flow restrictor, a first axially removable printing sleeve fitting over the first printing cylinder, a second printing cylinder having at least one second external hole and a second flow restrictor, a second axially removable printing sleeve fitting over the second printing cylinder, and a fluid supply source for supplying pressure to the first and second external holes. The first flow restrictor restricts flow through the external hole as a function of an axial position of the first printing sleeve with respect to the first printing cylinder and the second flow restrictor restricts flow through the second external hole as a function of an other axial position of the second printing sleeve with respect to the second printing cylinder.
Advantageously, complicated valves are not required between the first and second external holes.
The printing press preferably is an offset lithographic printing press, and the first printing cylinder a blanket cylinder.
Also provided is a method for axially removing a printing sleeve over a printing cylinder comprising the steps of applying fluid pressure to an inside of a printing sleeve located on a printing cylinder through holes at a work side end of the printing cylinder and through other holes between the holes at the work side end and a gear side end of the printing cylinder, sliding the printing sleeve in a direction of the work side end of the printing cylinder, and automatically restricting flow through the other holes when the printing sleeve no longer is located over the other holes.